1. Field of the Invention
The present invention relates to a chip with an IC (Integrated Circuit) and a micro-silicon condenser microphone integrated on a single SOI (Silicon On Insulator) substrate and a method for fabricating the chip.
2. Description of Related Art
Microphone is a transducer for changing sound signals into electronic signals. The traditional silicon condenser microphone typically includes a diaphragm acting as one electrode of a variable capacitance and a backplate acting as the other electrode of the capacitance. With sound signals entering the microphone, the diaphragm is deformed under influence of the sound pressures of the sound signals, which changes the capacitance between the diaphragm and the backplate. As a result, the change of the capacitance is transformed into the electronic signals by the subsequent processing circuits.
Since Electrets Condenser Microphone (ECM) was firstly invented by scientists of Bell Laboratories in 1962, with several decades development, the ECM has been widely used in multiple kinds of fields. The ECM has stored charge either in its backplate or diaphragm. However, such stored charge is easily leaked under high temperatures up to 260 degrees during automotive assembly. So, the ECM can only be mounted to a PCB by hand. With fast development of consumer electronics, such as mobile phones, PDAs, MP3 players and digital cameras etc., the ECM is losing its competition in such consumer electronics.
MEMS (Micro Electro Mechanical Systems) is a new technology rapidly developed in recent years. MEMS technology adopts advanced semiconductor fabrication processes and can realize mass production of MEMS components. Because of its potential advantages in miniaturization, performance, reliability, environmental endurance, low cost, mass production capability and high-temperature resistance capability, the MEMS component has been widely recognized as the next generation product to replace the conventional ECM.
Unlike the ECM, the micro-silicon condenser microphone fabricated by the MEMS technology depends on the external bias voltage to pump the required charge into its variable capacitor. As a result, the micro-silicon condenser microphone is needless of worrying about leaking of the stored charge. Since the micro-silicon condenser microphone can endure high temperatures during surface mountable installation, it can be automatically assembled on the corresponding PCB instead of hand installation.
In a convention method, the MEMS component and the IC are integrated by multiple substrates. That is to say, different companies adopt different processes to independently make the MEMS component and the IC on different substrates, and then the MEMS component and the IC are integrally packaged to a functional unit. Understandably, the conventional multiple substrate integration needs easy fabrication technique and the MEMS component and the IC can be optimized separately. Such multiple substrate integration has been widely used in kinds of MEMS component integrations, such as piezoresistance type sensors.
However, regarding some special applications, e.g. piezoelectric or condenser sensors with high output impedance, single substrate integration of the IC and the MEMS component has more advantages. The single substrate integration is capable of improving integral capability of the integral component and decreases influence of disturbing noise. The micro-silicon condenser microphone has characteristics of high output impedance, while it is easily influenced by the environmental disturbing noise and parasitic capacitance. Comparing with the multiple substrate integration, the single substrate integration of fabricating the micro-silicon condenser microphone greatly improves its integral component capability, dimension and power consumption.
Nowadays, there are three kinds of methods of single substrate integration. The first method is to fabricate the MEMS component first and then finish the fabrication of the IC on a same single substrate. The second method is interlaced fabricate the MEMS component and the IC are on the same single substrate. The third method is to fabricate the IC through standard semiconductor processes and then to fabricated the MEMS component on the same substrate. However, the IC manufactured by the first and the second methods is easily polluted by the prior MEMS component. The third method can avoid the pollution in the first and the second methods, and the third method can use existing standard semiconductor processes and reduce equipment investment. Regarding the third method, after the IC is fabricated on the substrate, high temperature must be avoided in subsequent steps for fabricating the MEMS component because the metal electrodes of the IC cannot endure high temperatures over 400 degrees. However, in the conventional MEMS technology, polycrystalline silicon is usually adopted as a structure material and the temperature of fabricating the polycrystalline silicon usually surpasses 400 degrees.
Hence, it is desirable to provide an improved chip with an IC and a micro-silicon condenser microphone integrated on a single substrate and a corresponding method for making the chip.